The sliding clamp protein PCNA, Aurora-A, Aurora-B, Borealin, and various topoisomerases can be SUMOylated (reviewed in Wan et al. 2012). SUMOylation of PCNA appears to reduce formation of double-strand breaks and inappropriate recombination (reviewed in Watts 2006, Watts 2007, Dieckman et al. 2012, Gazy and Kupiec 2012). SUMOylation of Aurora-A, Aurora-B, and Borealin is necessary for proper chromosome segregation. SUMOylation of topoisomerases is observed in response to damage caused by inhibitors of topoisomerases.